A prospective epidemiological study on subsequent cancer risk, by site, among cohorts of individuals undergoing tonsillectomy/adenoidectomy and/or appendectomy between 1925 and 1936 is continuing. Because a large proportion of the cohorts can now be expected to be deceased, a reliable and valid estimate of specific cancer risks according to type of lymphoid tissue surgery is expected to be generated. At present, major efforts are continuing to trace the cohorts as completely as possible to death or to survival as of a recent date. Also continuing is a preliminary analysis, among individuals already traced, of specific cancer risks. The prospective design of this study permits the estimation of true cancer risks, as opposed to the relative risks or odds ratios which must be relied upon in retrospective studies.